It is known to inflate a vehicle occupant protection device to help protect a vehicle occupant. The vehicle occupant protection device is inflated by inflation fluid from an inflator. One particular type of vehicle occupant protection device is an inflatable curtain that is inflatable into a position between the vehicle occupant and the side structure of the vehicle to help protect the vehicle occupant in the event of a side impact to the vehicle and/or a vehicle rollover. It may be desirable for the inflatable curtain to remain inflated for an extended period of time.